When I hit the brakes my engine idles real low (it does it just barely to hear it, you have to be listening, but it still bugs me) then back to normal (happens very fast tho). And makes a hissing noise, I find that it is coming from my brake booster or master cylinder. I sprayed engine start all around the brake booster but nothing. I located and fixed some vacuum lines and searched everyone of them. It is definitly not a vacuum (hose/line) leak. The noise or hissing is coming from the brake booster (i was tolded it moved too but I was the one hitting the brake so I didnt get to see it). Is this a sign to replace the booster or is it ok? Does anyone elses do this? What could it be?

Thanks,
Mario

 

maybe a leaking diaphragm in the booster in that case its time for a new booster. try unpluging the vacume line running to the booster and pluging it with something and then listen for the noise. good luck

 

Unplug the vacuum line to the booster from the plenum and suck on it. It should hold perfect vacuum.

 

When I unplug the vacuum hose that goes into the booster all the air shoots out, is this right?

Mario

 

Alright, I sucked on it and I got air out but toke it right back in. I plugged it and it still did it. I watched my engine and booster when somebody hit the brakes the booster doesnt move, the engine does it moves like there is a miss? And still makes a hissing noise. Where or what else could this be, and agian it only happens when the brakes are applied.

Mario